Electrolytic grinding apparatus



Feb. 26, 1957 G. E. COMSTOCK 3D ELECTROLYTIC GRINDING APPARATUS 3Sheets-Sheet 1 Filed April 15, 1953 HHU INVENTOR, [Em/v55 E. 50M57Z70K3rd BY M4 41am ATTORNEY Feb. 26, 1957 ca. E. coMsTocK 30 2,783,199

ELECTROLYTIC GRINDING APPARATUS Filed April 13, 1953 3 Sheets-Sheet 2//V5ULATION I INVENTOR. EEOR'GE E. 6'0M5T0LK 3rd.

ATTORNEY Feb. 26, 1957 G. E. COMSTOCK 3D ELECTROLYTIC GRINDING APPARATUS3 She ets-Sheet 3 Filed April 13, 1953 QWLUR hum 520355 6.. DansracK5117(- A TTOENEY United States Patent ELECTROLYTIC GRINDING APPARATUSGeorge E. Comstock 3d, Holden, Mass., assignor to Norton Company,Worcester, Mass, a corporation of Massachusetts Application April 13,1953, Serial No. 348,285

15 Claims. (Cl. 204-218) This invention relates to electrolytic grindingand more particularly to a system and apparatus for effecting stockremoval electrically from a conductive work-piece face.

One of the objectsof this invention is to provide a system and apparatusof the above-mentioned nature that is well adapted for ease andconvenience of installation in factories or plants already provided withalternating current circuits or sources and that is of dependablecontrol or regulation to effect eflicient stock removal electricallyunder widely varying conditions of practical requirements and use and isof desirable simplicity in manual setting. Another object is to provide,in a system and apparatus of the above-mentioned nature, controls of theflow or conversion of electrical energy for stock removal so as toprovide, at the locus of electrical stock removal, voltage and currentcharacteristics best suited for dependable, safe and eificient stockremoval with reliable and efficient variation in current regulation forwidely varying conditions at the above-mentioned locus.

Another object is to provide a system and apparatus for effecting stockremoval from a conductive work-piece by electrolytic decomposition atthe work-piece face and to provide for dependable and flexible controlof the conversion of alternating current energy to unidirectional ordirect current energy at the locus of electrolytic decomposition inorder to provide thereat voltage and current characteristics of thedirect current energy best suited for eflicient and safe stock removal.Another object is to provide a system and apparatus of the justmentionedcharacter in which the widely varying conditions at the locus ofstockremoval, caused by the exigencies or requirements met with in practice,efiect control of the voltage and current characteristics, andparticularly current control in relation to voltage control, in athoroughly dependable and quick-acting manner, of the direct currentenergy at the work-piece face so as to provide good safety andefiiciency of operation. Another object is in general to provide animproved grinding apparatus and control system for electric stockremoval at the workpiece face, in which current-limit level may bedependably changed automatically as required by changing conditions atthe work-piece face, such as changes in area, real or apparent, changesin resistance thereat, etc.

Another object is to carry out the above-mentioned objects, severally orjointly, in which the apparatus and system effect reliable controls ofthe electrical energy at the work-piece face and also under open-circuitcondi tions as when that work-piece and companion electrode element orelements are separated and particularly when they are brought together.Another object is to carry out the above-mentioned objects, severally orjointly, in which the apparatus and system, supplied initially from analternating current source, effect, in a simple and dependable manner,controls at the direct-current locus of work-piece decomposition orerosion that guard against initial current surges or flashes that wouldotherwise take 2,783,199 Patented Feb. 26, 1957 ice 2 7 place when thework-piece is brought in co-acting relation at the above-mentionedlocus.

Other objects will be in part obvious or in part pointed outhereinafter.

The invention accordingly consists in the features of construction,combinations of elements, arrangements of parts and in the several stepsand relation and order of each of the same to one or more of the othersthereof, all as will be illustratively described herein, and the scopeof the application of which will be indicated in the following claims.

In the accompanying drawings, in which are shown illustratively themechanical and electrical features of my invention and in which similarreference characters refer to several parts throughout the several viewsof the drawings.

Figure 1 is a front elevation, with certain parts shown or indicateddiagrammatically, of the grinding machine;

Figure 2 is a fragmentary side elevation thereof;

Figure 3 is a fragmentary horizontal sectional view on an enlargedscale, showing certain mechanical and electrical features of one form ofgrinding wheel in relation to a work-holder and certain electricalfeatures related thereto;

Figure 4 is a fragmentary or detached front elevation of a wheel guardcover and associated electrolyte-distributing parts as related to thegrinding wheel of Figure 3 and as seen from the front'in Figure 1 andfrom the left in Figure 3; and

Figure 5 is a diagrammatic representation of the apparatus, includingthe conductive wheel element of Figures 14, and the electrical energysupply system associated therewith and of the co-acting controlstherefor.

As conducive to a clearer understanding of certain features of myinvention it may here be noted that there are many advantages to begained in stock removal by electrolytic grinding in which, by theco-action of an electrolyte and direct or unidirectional current, stockis removed from the work-piece by electrolytic decomposition of the workface, especially for machining hard cemented carbides (such ascobalt-bonded tungsten and/or titanium carbide) whereby, when therotating conductive element or face of the grinding wheel containsabrasive grain, the cutting action of the abrasive grain may be verymaterially supplemented. Most industrial plants or factories areequipped with or wired for alternating current energy, usually andillustratively three-phase and of 60 cycles. One of the objects of myinvention is to provide efficient and dependable electrolytic grindingapparatus and compact, simple, and co-acting controllable energy supplysystem that needs only to be electrically connected to the existingalternating current supply lines and controllably furnish, at the locusof stock removal, the required unidirectional current or electrolyticaction. As heretofore attempted to be practiced, so-called electrolyticgrinding has encountered various difiiculties or the systems orapparatus have inherent limitations or there arise phenomena detrimentalto or destructive of the grinding wheel, and these handicaps become allthe more serious where, as is frequently the case, it is desirable touse diamond grinding wheels, which are costly. Another aim of thisinvention is to avoid or alleviate such handi caps, shortcomings orrisks and to provide more flexible and more efiicient controls, inresponse to changes in harmful direction of the electrical conditions atthe locus of electrolytic decomposition of the work-piece, at greaterstock removal capacity, of the conversion of the alternating currentenergy, whether or not electrolytic decornposition is accompanied byabrasive action.

In stock removal by electrolytic decomposition at the work face, theconductive work-piece is made the anode, and at the work-wheelinterface, where there may or may not be physical contact and wherethere may or may not be accompanying abrasive action, there isadequately supplied a suitable electrolyte, which also serves as acoolant, and it is desirable to use high current density since the rateof electrolytic decomposition at the work-piece face is proportional tocurrent flow. Various conditions can occur or be brought into being atthe work-wheel interface that will cause detrimental actions, such asarcing, current surges, high-intensity flashes, etc., which can alsocause damage or cause excessive rates of wheel wear which, particularlywhere diamond abrasives are embodied in the wheel, can proveprohibitively costly. It can be shown that a desirable characteristic ofsupply of direct current for the electrolytic circuit is one where thevoltage across the work-wheel interface is maintained sub stantiallyconstant up to the point where the electrolytic current flow approachesa critical value above which deleterious arcing occurs, followed bycurrent-limiting action at a selectable current value less than thecritical current, to reduce the voltage across the work-wheel interfaceto prevent the current from reaching or exceeding the critical value. Afurther object of this invention is to effect conversion of alternatingcurrent electrical energy into direct current energy at the work-wheelinterface with the energy conversion controlled, in response toconditions at the work-wheel interface so that the just-describedcharacteristic of energy supply at the work-wheel interface is providedin a simple, compact, efiicient and reliable manner and moreover in amanner to vary the level of current control automatically to meet avariety of varying or variable conditions, both at starting and runnmg.

In describing my invention I prefer to do so in connection with anelectrolytic grinding apparatus in which the grinding wheel, whileconductive, also contains abrasive grains and also because certainprotective actrons which the system of my invention achieves serve alsoto excellent advantage where both electrolytic and abrasive action takeplace conjointly, as is frequently desirable in practice. Any suitablemechanism or arrangement may be employed for mounting and driving theconductive grinding wheel and for mounting or supporting, or even forresting thereon for manual movement (as in so-called off-hand grinding),a work-piece, such as a cemented carbide tool or other piece of work orobject to be ground or machined, whereby to obtain relative movementsbetween the grinding wheel and the supported work. Many and variousforms of mechanism are well known for cooperatively relating a grindingwheel and a work-piece for relative movement therebetween and providingfor various relative adjustments and/ or movements between the grindingwheel spindle and the work together with various manual or automaticcontrols for such adustments and movements. For example, I may utilize amachine such as is shown in U. S. Patent 2,101,781, in which awork-table, underlying an adjustably mounted and rotatively drivengrinding wheel spindle, is movable and reciprocable relative to thegrinding wheel and is mounted on a cross slide for shifting ittransversely, that Is, forwardly or rearwardly of the machine, relativeto the grinding wheel; in the machine of that patent the work-table canbe reciprocated upon the transverse or cross slide by manual means or byfluid pressure mechanism as there described, while the cross slide maybe man ually or mechanically moved to advance the work-table and thework-piece supported by it in steps or at a rate according to thesetting of the infeed mechanism or according to the manual actuationthereof, as by a hand wheel. Or, I may utilize a grinding machine, byway of further illustration, of the type or kind disclosed in Patent2,381,034, the machine of that patent being particularly adapted toshaping tool bits, particularly bits or tools of the above-mentionedhard cemented carbides, and in that machine the operator manually shiftsthe holder or carrier that supports the work-piece or tool, relative toan adjustable table or support and relative to the flat side face of thegrinding wheel, according to various curvatures of surfaces or fiatsurfaces, sometimes with the aid of templates or with the aid of variousadjust ments of various angularities, according to the specificcharacter of surface shaping that the particular tool or tool bitrequires. These two patented disclosures are illustrative of two of themany types of grinding machines to which our system and controls areapplicable for effecting stock removal by electrolytic decomposition atthe face of the work-piece.

Accordingly, in the drawings, I have shown in Figures 1 and 2, a drivingmounting forthe, rotating conductive element together with anillustrative work-piece and workholder or support, with a work-table forthe latter depicted largely diagrammatically, particularly insofar asits adjustability and movement relative to the rotating grinding wheelare concerned, inasmuch as much adjustability and movement, and themechanism for effecting them, may take any suitable or known form, andmany thereof are well known in the art.

Thus, the apparatus may have a base or main frame 10 which, at its rear,supports a column or vertical standard 11 which, as indicated by thearrows thereon, is rotatively adjustable about a vertical axis and isalso adjustable in up-and-down direction; the column 19 supports a wheelhead 12, in which is journaled a grinding Wheel spindle 13 whichprojects both forwardly and rearwardly of the wheel head, and at itsrear end carries a pulley 14 which is driven by a belt 15 from a pulley16 on the shaft of a motor 17, which is suitably carried by the top ofthe standard 11.

The front end of the spindle 13 is appropriately con structed to have oris provided with means for mounting a grinding wheel thereon, as byproviding it with tapered portion 21 (Figures 3-6) that is received intothe tapered bore of a flanged sleeve 22, a nut 23 which is threaded ontothe spindle 13 holding the flanged sleeve 22 securely in place. Theflanged sleeve 22 is suitably constructed to carry and has securedthereto a grinding wheel which is electrically conductive and which isillustratively and preferably constructed, as is shown in Figures 3 and4 and as is later to be described.

When the grinding wheel is so mounted at the front end of the spindle3.3 it substantially overlies or overhangs a work-table 24, which isreversibly movable and reciprocable, as indicated by the double-headedarrow in Figure 1, being supported in suitable lengthwise extending waysprovided in the cross slide diagrammatically indicated at 25, the latterbeing adjustable or movable, reversibly, as indicated by thedouble-headed arrow in Figure 2, being suitably carried or supported,for that purpose, on suitable ways provided in the base 10.

The work-piece W, which for purposes of better illustrating certainfeatures of my invention, may be considered to be a block of cementedcarbide and suitable means are provided for releasably holding orclamping it to facilitate control of its movement relative to theoperative face of the grinding wheel, and such means may comprise aheavy-worit-holding bar 27, which is provided with a suitable hole orrecess 23 in which the work W is received and in which it is clampedsecurely, as by a clamping screw 29. in the electrolytic grindingcircuit the work W is to serve as the anode in the electrolytic cell andaccordingly suitable provision is made for connecting the work Wappropriately into the electrical circuit, and such means may comprise asuitably heavy connector screw 30 by which a conductor may be clamped,carried by and threaded into the work'holding bar 27, as is betterindicated in Figures 3 and 5. The work-holding bar 27 may in turn becarried "by a visc, generally indicated at 31; the vise may be of anysuitable construction and may, for example, comprise a fixed vise jaw 32and a movable clamped and held, as by the screw 34, manually operable,

as by the handle 35. The vise 31 can rest on the worktable 24, withwhich, when suitably secured thereto, it is movable according as thework-table 24 is moved or actuated as in the above-mentioned Patent2,101,787, or relative to which the vise may be manually moved, as inthe above-mentioned Patent 2,381,034, in either case to effect thedesired or controlled traversing movement or movements of the work Wrelative to the grinding'wheel and to effect the desired feeding and theretracting movements thereof relative to the wheel. As indicated in thedrawings, we may provide suitable means such as bolts 36 for clampingthe vise 31 at any desired angularity to the work-table 21, where it isdesired that the vise move with the table, the bolts being simplyomitted when it is desired to manually shift or control the movements ofthe vise and Work-piece W relative to the table. In Figures 1 and 2 thegrinding wheel is generically indicated by the reference character CR,and by way of illustration but not by way of limitation it isconstructed to present a conductive ring surface 'at its flat annularsideface which, according to the rotational setting about its verticalaxis, of the column 11 which supports the wheel head 12, may be givenany desired angularity relative to the longitudinal path of movement ofthe movable work-table 24, according to the needs of any particulargrinding job, but for greater simplicity of description the wheel headmay be considered as set so that the plane of the operative annular sideface of the wheel extends parallel to the line .along which thework-table 24 is movable or rcciprocable.

A suitable wheel guard 38 is provided, being secured to :the wheel headby suitable brackets 39 and being provided 'with a hinged front cover 40so that access to the wheel spindle 13 may be gained for mounting ordemounting the grinding wheel; the wheel guard with its cover 40 may beshaped substantially as shown in Figures l-4, being cut away as shown toexpose a suitable portion of the front face of the wheel where theconductive ring surface is operative and so that the work W may bepresented thereto, and to expose a complementary back portion of thewheel for purposes about to be described.

Suitable means are provided to supply a suitable electrolyte to theregion of contact or of juxtaposition between the grinding wheel CR andthe work W; such means may comprise a broad-mouthed nozzle N, which ispreferably adjustably positionable, as by a suitable length ofdeformable metal tubing 41, which is connected to and supported by arigid pipe 42 secured to the wheel guard as indicated (see also Figure4). Accordingly, deformable tube 41 may be manually bent and set to givethe nozzle N the desired location, the mouth of the nozzle beingappropriately dimensioned to discharge the liquid electrolyte at andthroughout the entire width of the conductive ring surface of the WheelCR, where the Work-piece W is presented to the latter.

In Figure l I have shown a tank 44 containing liquid electrolyte 45; thelatter can be a solution of sodium chloride in water, preferablyreasonably concentrated; for example, when the tank is full of purewater, a surplus of common salt may be added thereto so as to leave aquantity of undissolved salt which simply rests on the bottom of thetank. Other salts can be used, but for keeping corrosion at a minimumthe very corrosive salts, such as calcium chloride, magnesium chlorideand sodium chloride are preferably avoided. Salt, such as sal ammoniacammonium chloride) can be used. The carbonates, such as sodiumcarbonate-and potassium carbonate, can be used and in some cases may bepreferred, as they are somewhat less corrosive than sodium chloride.

Mounted on the cover plate 46 of the -tank 44 is an electric motor 47which drives a pump 48, the input end of which is connected by a pipe 49to the inside of the tank 44, with the open end of thepipe beingpreferably near the bottom of the tank. The output end of the pump 48 isconnected by suitable piping 50, and a suitable length ofrflexi'ble hose51 to a valve 52 on the end of the pipe 42 which is secured to thehinged wheel guard cover 40. An arrangement such as just described maybe used to supply the work-wheel interface adequately with electrolyte;from that location the electrolyte copiously runs out of the bottom ofthe wheel guard and it and any drippings thereof are eventuallycollected by a large pan 53 which is built around the top edge of theWork-table 24, and as shown in Figure 2, a spout 54 carried by thework-table and movable therewith discharges the pan-collected liquidinto a stationary pan 55 that is suitably supported by the base 10 ofthe machine and which extends throughout the full length of maximumtravel of the spout 54 as the latter moves with the work-table. A returnpipe 56 extends from the pan 55 to the tank 44.

The wheel CR may be of any suitable construction and has a suitableconductive element or face, which I arrange to co-act in effecting, inthe electrical energy conversion and supply system, control ormodification of the alternating current energy to provide direct currentenergy of the earlier above described characteristic of substantiallyconstant voltage across the work-wheel interface followed by currentlimiting action with diminished voltage so that critical current valuesare not reached or exceeded. Illustratively the wheel of my system andapparatus may have-a single conductive face and illustratively, for thatpurpose, maybe constructed as shown in Figures 3 and 4 about to bedescribed in detail.

Referring now to Figures 3 and 4, the single-conductive-faced wheel isthere generally indicated by the reference character 60, and in orderalso to gain certain advantages in achieving electrical insulation orisolation, the wheel 60 comprises a strong rigid backing B of anysuitable cured plastic or the like, such as Bakelite resin; at itscenter it has molded into it a hole (Figure 3) so that it can bereceived onto the flanged sleeve 22. As better appears from Figure 3,the backing B has an outer rim-like or annular portion which is ofgreater thickness than the central portion which is received onto theflanged sleeve 22 and which is clamped between the flange and thespanner nut 61; this outer portion of greater thickness presents anannular side face, being the left side face as viewed in Figure 3 andbeing the front face as viewed in Figure 4, and at that face andpreferably coaxially therewith the wheel 60 carries a conductiveabrasive ring CR1 which presents, in the illustrative construction, anannular conductive face with which the workpiece W and the electrolytecan co-act. This ring CR may be secured to the backing B in any suitablemanner, but preferably the ring is constructed so that it is embedded inthe non-conductive material of the backing B and preferably it isassembled to the backing itself when the latter is initially molded outof the uncured resinous material which is, during the molding process,made to flow about the faces of the ring except its operative face andto become interlocked therewith upon curing of the resinous or otherplastic, as under heat and pressure; for better interlocking the ring CRmay be of a conformation that provides a continuous annular dovetail D(Figure 3), which can be integrally formed at the back of the ring.

As above indicated, it is sometimes desirable that the rotatingconductive element in electrolytic grinding contain abrasive grains andthe wheel 60 may be constructed also in a manner to facilitateembodiment of abrasive grains when and where desired. For the grindingof hard cemented carbides, such as those illustratively mentioned above,suitably bonded diamond grains, as a bort, are usually employed becausesilicon carbide abrasive grains are hardly as effective on cementedcarbides, while alumina grains grind them hardly at all. While, in theillustrative embodiments of my invention I prefer to use diamondabrasive grains, grains of other materials,

including silicon carbide and aluminum oxide, may be employed, and. asis later made clear, in electrolytic grinding, stock removal may beeffected solely by electrolytic decomposition ofthe metal at thework-face Without any material abrasive action by any of the grains inthe rotating conductive ring or face. Where grains are employed, inorder that the ring CR be conductive, the abrasive grains aremetal-bonded, and particularly where diamond'grains are employed it ispreferred that they be embodied in only a relatively small depth inrelation to the overall thickness of the ring itself and accordingly, asis clear from Figure 3, the ring CR comprises an outer abrasive orgrain-containing portion 6201? small thickness or depth, and an innerand usually thicker and heavier portion 63 that need not contain anygrains and is of metal throughout, serving as a strong rigid support orbacking for the thinner diamond-bearing portion 62. Where a dovetailelement D is employed, it forms part of the metal backing portion 63, asshown in Figure 3, and may be integrally formed or molded therewith orturned or machined to the desired shape.

In making the conductive abrasive ring CR any suitable or known methodsor techniques may be employed and need not be described in detail here.For that matter, the patented art describes how, with the use ofpowdered metal, to make up a unitary integral abrasive ring or annulushaving an outer diamond-bearing abrasive portion and an inner supportportion wholly of metal. I might note, however, that a usual method ofmanufacture comprises placing in a suitably shaped mold, to the desireddepth, powdered metal that is to correspond to the non-abrasive backingportion and, after leveling or smoothing off, placing thereover asuitable depth of a mixture of diamond particles and powdered metal, tocorrespond with the abrasive portion and, after leveling or smoothingoff, subjecting the contents of the mold to substantial pressure andthen sintering the pressed piece, usually in a protective atmospheresuch as hydrogen. By appropriately shaping the mold parts the backingportion 63 may be conformed to have a projecting dovetail part or ring,such as the dovetails D of Figure 3, or, as above noted, and since thebacking portion 63 contains no abrasive grains, the dovetails D need notbe formed by molding but can be turned or machined to the desired shapeafter pressing and sintering are completed.

Any suitable metal bond appropriate for bonding the abrasive grains andfor giving the rings suitable electrical conductivity may be used. Inthe abrasive-containing portion of each ring. such as the portions 62 ofFigure 3, the concentration of abrasive grains should, of course, not beso great as to detrimentully affect electrical conductivity. For finelydivided diamond as the abrasive grain, a concentration thereof in theabrasive portion on the order of 25% or less by volume is suitable. Ofthe many and various metals that are usable for metalbonding the diamondgrains, i prefer to employ a mixture of copper and tin powders in theproportion of about 82% copper and 18% tin, making for both excellentelectrical conductivity and good bonding of the grains, and this samemixture of copper and tin is employed in making up the non-abrasivebackings, such as the portions 63 of Figure 3, and I set out the justmentioned mixture of copper and tin as an illustration.

The wheel 60 is driven in clockwise direction as viewed in Figures 1 and3, at a suitable speed to give its conductive ringface suitable surfacespeed for appropriate abrasive action, and suitable means are providedto electrically connect its conductive ring CR into the electricalcircuit so that the conductive ring is the cathode, for electrolyticdecomposition at the face of the work-piece W; such means convenientlycomprises a slip ring constructed and coaxially mounted for rotationwith the grinding wheel spindle 13, and a suitable coacting mounting forsupporting a brush that bears against the slip ring.

In Figure 3 I have shown such a slip ring as S and it is preferablycarried by the non-conductive backing the conductive ring CR isoperative.

back B has been molded and curved with the ring CR v interlocked, at thefront face, with the cured molded in sulating material, and then securedin position by a suitable number of vequi-angularly spaced tensiontie-members 65, which extend through suitable holes in the back B andare anchored, as by threading, at their inner ends to the conductivering CR in which tapped holes are.

provided in the backing portion 63 thereof; the outer ends of thesetie-members, which preferably take the form of long screws preferablymade of copper or of a coppertin alloy, extend into suitable countersunkholes in the:

slip ring S thus to clamp the latter securely and concentrically inposition at the back face of the wheel back B and at the same timeforming multiple electrical connections of high-current-carryingcapacity between the slip ring and. the conductive ring CR The screwsmay be headed, in which case the heads are countersunk into the sliprings, or the screws may be headless, in which case those portions thatextend into the countersunk holes in the slip rings may be radiallyexpanded by pressure or by peening to fill up the tapered holes in theslip ring, the taper being appropriately proportioned to the cold-flowcharacteristics of the metal of the screw shank to facilitate cold-flowexpansion thereof as just mentioned. The faces of the slip rings maythen be machined, as by turning in a lathe, or by grinding, to

be sure that they fall in a plane at right angles to the axis of thegrinding wheel and to be sure that the ends of the screws 65 are flushwith the faces of their respective slip rings, thus to insure smoothcoaction with the brushes of the circuits in which the parts are tocoact.

As is better shown in Figure 3, the wheel head 12 has secured to it, asby cap-screws as shown, a bracket 66 which extends in a radial directionrelative to the grinding wheel 60 and which is constructed in anysuitable way to insulatingly support a brush 67 which is spring-pressedto the left to bear against the face of the rotating slip ring SSuitable means are provided, such as a connector screw 68, forelectrically connecting the springpressed brush 67 into theenergy-supply and control circuit arrangement of our system, which isdiagrammatically shown in Figure 5.

In Figure 5 the conductive abrasive ring CR with the work W presented toit, are diagrammatically shown, as are also the slip ring S and brush 67as well as the connector screw 30, for electrically connecting the workW to one side of the direct-current energy-supply circuit and connectorscrew 63 for connecting the brush 61 to the other side thereof. InFigure 5 I also indicate an alternating current power circuit, which maybe any of the types usually found in factories or industrial plants, andit may be singleor multiple-phase; for illustrative purposes, it may bea three-phase power supply line, usually 60cycle, and of any suitablevoltage; illustratively 440 volts, and in Figure 5 this power line isrepresented by the reference characters 2 p 2 From such a power line orsource of alternating current supply, I make provision for convertingalternating current energy to direct current energy supply for coactionwith the anodic Work W and the rotating wheel ring CR with theelectrolyte between the latter, for electrolytic decomposition at theface of the work W, all in a manner and under coacting controls toachieve a number of advantages and safeguardagsome oi -which have beenindicated earlier above.

In Figure the broken-line rectangle MA, with the parts diagrammaticallyshown within it, represents a magnetic amplifier of the self-saturatingtype constructed and arranged for A. C. input and for D. C. output, withappropriate rectifiers and control windings. While the magneticamplifier MA as well as other such devices later described, are shown asarranged for three-phase alternating current energy input, that is notto be interpreted by way of limitation but rather as illustrative,inasmuch as these self-saturating magnetic amplifiers serve our purposesalso when arranged and constructed for A. C. input of other thanthree-phase, such as single-phase, two-phase, etc.', and theirfunctioning, coactions and controls are essentially the same as, and arewell-illustrated in, the three-phase structures herein disclosed.

In Figure 5 the magnetic amplifier MA comprises a suitable number ofreactor units, six in number, for threephase A. C. input,diagrammatically shown at I, II, III, IV, V, and VI, each reactor unitcomprising a gapless laminated core of steel of very high permeability,diagrammatically indicated in Figure 5, each core being linked by powerof output windings and by appropriate control and/ or biasing windings.In the illustration each reactor unit has a power winding PW, and theseare interconnected with rectifiers RF in the manner shown, with thethree-phase power line p p p connected by conductors 71, 72, '73respectively to the input terminals of the magnetic amplifier MA thoseinput terminals being respectively, as shown, between adjacent pairedrectifiers RF--RF; direct current energy output is delivered at theoutput terminals 74, 75, leading from the interconnected power windingsPW, as shown in Figure 5.

The above described parts of the magnetic amplifier MA are, in each ofthe reactor units, so proportioned to each other that wheninterconnected as shown and as above described they will be capable ofdelivering a direct current output which, illustratively, can be on theorder of 24 volts at an amperage on the order of 150 amperes, whenenergized on the input side by three-phase alternating current of 60cycles at suitable voltage; since the construction, action and operationof such a self-saturating magnetic amplifier are known, these aspectsthereof need not be in detail herein described. It might, however, benoted that the just described magnetic amplifier MA is commerciallyavailable. may be on the order of 32 volts, in which case a stepdowntransformer T is interposed as is diagrammatically indicated in thedrawings.

However, the peculiarities and variables that are vir tually inherent inthe actions or coactions that take place across the interface wherestock removal from the workpiece, W is electrically effected impose anumber of difficulties and handicaps which work against simplyconnecting the D. C. output of the magnetic amplifier across thework-wheel interface, particularly if the desired precision of grindingand safety or protection for the wheel conductive element and thework-piece are also sought, and accordingly I have made readilyadaptable provisions and relatively simple coacting circuit arrangementsfor dependably controlling the conversion of alternating current energyto electrical energy of voltage and current characteristics that aredetermined and controlled by the variables that occur at the work-wheelinterface. These provisions and circuit arrangements will now bedescribed.

In the illustrative embodiment I provide each of the six reactor unitsI, II, III, IV, V, VI with three control windings BW, RW, CW, which areenergized in a manner later described to affect the saturable cores ofthe reactors. The windings BW of the several reactor units are connectedfor conjoint or simultaneous energization, as by connecting them inseries as shown, their common cir- Its A. C. input voltage cuitterminating at terminals 79, 76. In similar manner the several windingsRW are interconnected, the resultant circuit terminating at terminals77, 78. Windings CW are also in similar manner interconnected, withconnecting terminals at 81, 82. Windings BW are bias windings which,when energized, bias the several reactor units in known manner, beingenergized by unidirectional current.

For this latter purpose and for other purposes latter explained, I makesuitable provision for deriving unidirectional current energy from thepower line 12 11 p For example, from one of the phases of thethree-phase power circuit I connect, as by conductors 82, 83, a voltageregulator or stabilizer VS, which may be of any suitable or knownconstruction to provide at its output 60-cycle alternating currentenergy at a fixed or constant voltage, such as 115 volts, in order thatthereby variations or fluctuations in the voltage of the three-phasesupply be not reflected in the control circuits of the system;accordingly, conductors 84, lead from the output side of the voltagestabilizer and provide a constant voltage circuit, from which relativelysteady potentials may be provided and utilized.

Across the steady voltage circuit 84, 85 is connected the primary of atransformer T whose secondary is connected as shown to the inputterminals of a rectifier bridge RB, across the substantially constantvoltage output terminals of which are connected conductors 86, 87,across which are bridged a number of resistors provided with taps sothat the fixed voltage drop or constant unidirectional potential may befractionalized or subdivided as required or needed. One of theseresistors R serves to energize the bias windings B-W of magneticamplifier MA at the selected or desired potential derived from the fixedvoltage across the output circuit 86, 87 of the. rectifier bridge, inthat a conductor 88, connected to one side of the resistor R atconductor 87, leads to bias winding terminal 79, and another conductor89 leads from the other connecting terminal 76 through a protectiveresistance R to the adjustable tap on resistor R Accordi-ngly,energization of the bias winding BW of the power magnetic amplifier MAmay be manually set by appropriately shifting the tap on resistor RThe-control windings CW of the power magnetic amplifier MA having theirconnecting terminals at 81, 82, are preferably controllably energizedunder the control of a magnetic preamplifier MA which has aunidirectional current output at terminals 91, 92, which are connectedby conductors 93, 94, through a suitable resistor R to the terminals 81,82 of the control windings CW of the power amplifier MA like the latter,the preamplifier MA may comprise six reactor units diagrammaticallyindicated by the reference characters VII, VIII, IX, X, XI, XII, eachunit comprising a gapless laminated core composed of steel of highpermeability, with their respective output or power windings PWinterconnected with rectifiers RF as shown, the three-phase power linebeing connected by conductors 95, 96, 97 between the respective pairedrectifiers as shown, the unidirectional or direct current energy outputbeing furnished by connections as shown to the amplifier outputterminals 91, 92.

The preamplifier MA is provided with bias windings BW one for eachreactor unit, and they are connected for conjoint or simultaneousenergization as by connecting them in series as shown, with the commoncircuit terminating at terminals 98, 99. Unidirectional energizingcurrent for the bias windings, of selectable or adjust-- able value, isderived from the constant voltage rectifieroutput circuit 86-87, acrosswhich is connected a resistor- R provided with a s'hiftable tap; aconductor 100 con nects amplifier terminal 98, through circuit conductorMeans are provided for effecting coaction between thepreamplifier MA andthe power amplifier MA all underthe control and direction of thepeculiarly variable conditions at thework-wheel interface, for causingthe electrical stock removal action at the latter to take place atmaximum safe intensity; these include means for translating theseelectrical variables and include certain windings which I place on thereactors of the two amplifiers to respond thereto. To the D. C. outputterminals 74, 75 of the power amplifier MA I connect, by conductors104-, 105, the conductive wheel member CR and the workpiece W, thelatter being made anodic by connc2ting conductor 105 to the connectorscrew 30, and the con nection of the negative output terminal 74 of thepower amplifier to the conductive wheel member CR being made byconnecting conductor 104 to the connector screw 68 of the slipring brush67,

Across the D. C. power output circuit 104. HES l connect a resistor Rillustratively of about 3 ohms; resistor R provides a small load on theD. C. output side of the power amplifier MA so that the operation of thelatter and of associated circuits need not be undesirably atfected by anopen-circuit value of voltage were the direct current circuit actuallyinterrupted at the work-wheel inter face, as by removal of the work Wfrom coacting relation with the electrolyte and the conductive ring CRand accordingly there is always effective, across the workwheelinterface, a definite D. C. voltage even with no current flow throughthe electrolytic interface cell. An illustrative interface voltage forthis purpose may he, say, volts.

Various factors and variable at the interface can cause departures fromthe desired or most suitable values of D. C. voltage across thework-wheel interfact and of the current flowing thereacross for stockremoval from the workpiece W. Changes in applied voltage can beconveniently measured by the voltage across the small-load resistance Rin which they are reflected; certain voltage changes I make operative toaffect preferably the pro amplifier MA in a manner later described. As.for changes in current across the interface, I make provision forcausing certain response thereto to take place preferably in both thepower amplifier MA and in the preamplifier MA}; in this latterconnection I employ one or more interface-current-responsive deviceswhich. so .far as certain features of my invention are concerned, maytake any suitable form. lllustratively I may employ a device whichpreferably is in the form of a core CO that extends about or envelopsone of the conductors, such as conductor 104, that lead to theconductive wheel element CR and work-piece W, the core CO having thereona winding 106. The core CO may be of any suitable construction orarrangement, preferably and illustratively it is torus-shaped. and it ismade of transformer iron or steel of suitable permeability. The magneticfield produced by the current flowing in conductor 104 extendscircularly about the conductor, being coaxial therewith, and with thetorusshaped iron core CO positioned coaxially with the conductor 104,the core forms a high-permeability path for the flux and the fluxdensity in the core varies with the magnitude of the current flowingthrough the conductor. The parts are so proportioned in relation to thecurrent magnitudes that, as the interface ca is for increasing current,the core moves closer and closer to saturation on its permeabilitycurve. The action of the winding 1525 can in this manner be affected orvaried according as-interfacc current flow changes in magnitude.

Winding 106 is energized in an alternating current circuit and hence thejust-described action of the core affects and changes the impedance ofthe winding 106.

I provide a transformer T of which the primary is energized from thesteady or constant voltage circuit 84, 85 above described, and of whichthe secondary is connected in series with the winding 106 across theinput terminals, as shown of a rectifier bridge RB across the outputterminals of which are connected conductors 107, 108, across which, inturn, are bridged resistors R R the latter are thus energized byunidirectional current resulting from the full-wave rectification of therectifier bridge and at a voltage which changes as the voltage acrossthe input terminals of the bridge is changed by changes in impedance ofthe winding 106.

Resistor R is provided with a shiftable tap so that any desired fractionof the variable voltage thereacross may be made available, and such aselected unidirectional potential I utilize to energize the controlwindings RW of the power magnetic amplifier MA More particularly, aconductor 109 connects the amplifier ter minal 77 to one end of resistorR by way of conductor 108, and a conductor 110 connects the otherterminal 78 of the windings RW to the shiftable tap of the resistor R3,through a protective resistance R18, a shown in Figure 5.

The windings RW of the power amplifier MA are thus steadily energized byunidirectional current, but the effect of the windings RW on therespective reactor units of the power amplifier MA and upon the outputof the latter is under the control of the current flowing across thework-wheel interface, and in accordance with certain other features ofmy invention, later described, other controls are made to coacttherewith for purposes later described. Varying conditions at thework-wheel interface can and do call for substantial changes in currentflow thereacross. For example, at one point in a stock-removaloperation, as, for example, when the actual or apparent contact betweenthe work and the wheel is of relatively high resistance, current flowacross the interface may be small, but as that resistance is decreased,as by bringing about more intimate contact or increased pressure ofcontact, current flow substantially correspond ingly increases. Withresultant increase in current out put of the power amplifier MA theoutput voltage of the latter across the output terminals 74, falls offor declines, causing a drop in the energy dissipated at the work-pieceface and loss in rate of stock removal. At low values of interfacecurrent, unidirectional flux in the core CO is correspondingly low andthe impedance of winding 106 is high so that there is a relatively highreactance drop in the secondary output circuit of trans former T and thealternating potential applied to the input of the rectifier bridge RE iscorrespondingly low; accordingly, the unidirectional voltage across therectifier output circuit 107, 108 is low and the energization ofwindings RW of the power amplifier, derived from the resistor R is alsolow. When, however, the workwheel interface calls for increased currentflow thereacross the current of the increasing current flow increasesthe unidirectional flux in the core CO, driving the latter more and moretoward saturation and thereby correspondingly lessening the impedance ofwinding 106 and the impedance drop thereacr-oss so that more and more ofthe alternating voltage of the secondary of transformer T is efiectiveat the input terminals of the rectifier bridge RB correspondingly theunidirectional output voltage of the rectifier bridge and the voltageacross resistor R are increased, as is also the unidirectionalenergization of the windings RW of the power amplifier. The increasingenergization of windings RW affect the cores of the reactor units of thepower amplifier in directions to cause the unidirectional voltage at itoutput terminals 74, 75 to increase as against the inherent drop inoutput voltage that would otherwise take place. With th resultantcompensation for decline in output voltage of the power amplifier, thecall for increase in interface current as required by the changed orchanging conditions at the interface can be and is satisfied and loss inrate of stock removal avoided.

The arrangements just described has many advantages from the viewpointof structural elements involved in that the latter, such as the variableimpedance device.

comprising the winding 106 and core CO, the transformerT the full-waverectifier bridge RBliand tapped.

resistor R are relatively simple in construction, and the accompanyingcircuit arrangements are also relatively simple, all as will now beseen; moreover, these parts when interrelated as above described, witheach other and with the work-wheel interface achieve numerous practicaladvantages of coaction and operation; for example, varying or changingconditions at the work-wheel interface effect dependable andsubstantially propionate responses to current changes across theinterface and do so without material loss or wastage of energy flowingacross the interface, and it is possible to avoid substantial heatlosses in that oneneed not employ a series resistor in the work-wheelinterface circuit; thereby however, I do notv mean to exclude a resistorfrom the scope of my invention except where and as stated in the claims.Also, these responses are efficiently translated into proportionatevalues of voltage or current or both, such as the unidirectionalpotential across the rectifier output circuit 107, 108, which are of amagnitude appropriate or suitale for directly energizing controlwindings of the magnetic amplifier or amplifiers employed. In the abovedescribed embodiment the windings RW of the amplifier MA will be seen tobe directly energized from this circuit 107, 108, and this takes placeat variable voltage and current of magnitudes suited to the constructionof the power amplifier. For setting or changing the standard ofoperation for compensation of voltage drop in the output of the poweramplifier, the variable tap at the resistor R may be appropriately set.Also, the secondary winding of transformer T may be provided with a tapas shown, for similar purposes. Either or both may be set, according tothe range of change in standard of operation to be effected.

Coacting with the above, as above indicated, are other features, alsounder the dictation or control of the peculiarly varying conditions atthe locus of electrical stock removal from the work-piece face. Amongother control windings, preferably applied to the magnetic preamplifierMA are windings VW, one for each of the reactor units VII, VIII, IX, X,XI, XII and suitably connected, illustratively in series as shown, forconjoint or simultaneou energization, from the amplifier terminals 113,114, whereby the windings VW, in coaction with the bias windings BW maybe connected, as is about to be described, to achieve certain controlsover the voltage which the power amplifier MA applies to the workwheelinterface. Across the substantially steady or constant voltage circuit$6, 87 earlier above described I provide a resistor R that has a tap asshown, by which any portion of the voltage across the resistor R may beselected as a fixed or steady reference voltage against which to measurethe voltage across the work-wheel interface, a voltage which can changesubstantially according to various factors including changing conditionsat the work-wheel interface.

These two voltages, that is, the selected reference voltage tapped fromresistor R and the voltage across the work-wheel interface W-CR I bringinto coaction to control the energization of the preamplifier windingVW, in a circuit which extends from preamplifier terminal 113, thenconductor 115, a protective resistor 116, a unilateral valve orrectifier UV, resistor tap, then the selected portion of resistor Rconductor 87, conductor 117, and by brush 67 and slipring S to theconductive Wheel element CR which is one side of the work-wheelinterface, and from the work-piece W, which is the other side of theworkwheel interface, by way of conductor 118, to the other preamplifierterminal 114. In this circuit arrangement, as will be seen by the justdescribed circuit connections, the reference voltage set or selected bythe tap on resistor R and the voltage across the work-wheel interface,both unidirectional, are in opposition to each other. So long as thevoltage across the interface is less than the selected reference voltageat resistor R so that the fixed reference voltage determines thedirection in which current flow would take place in the described seriescircuit, which in cludes the preamplifier windings VW, current flow toand through the windings VW need not take place, for there need not beany interference with the self-control which the work-wheel interfaceconditions can variably effect through the windings RW of the poweramplifier MA as earlier above described, and accordingly the unilateralvalve or rectifier UV is included in the circuit to block current flowto the preamplifier windings VW.

The bias windings BW of the preamplifier are energized, by setting thetap on resistor R so that with no current flowing in the controlwindings VW the preamplifier MA is biased, and stands biased, at or justbelow cut-01f, so that the preamplifier has a zero output and hencecontrol windings CW of power amplifier MA are, and stand, de-energized.The bias windings BW of the power amplifier, by adjustment of the tap atresistor R are energized at a value to bias the amplifier above cut-offto provide unidirectional output, to the work-wheel interface, at thedesired voltage which, should it inherently fall off because of increasein interface current, the latter effects compensation for the voltagedecline by increasing the energization of windings RW in a direction toincrease the bias and thus correspondingly raise and substantiallyrestore the voltage across the work-wheel interface.

However, should the voltage across the work-wheel interface exceed thatof the selected reference voltage at resistor R so that the resultantdifference in voltage determines flow of current in reverse direction,the rectifier UV permits such flow to take place and the preamplifiercontrol windings VW are energized. The resultant energization ofwindings VW, in relation to the cut-off bias eifect of bias windings BWbiases the reactor units above cut-off and causes a current fiow at theD. C. output of the preamplifier at its terminals 91, 92 which areconnected to the control windings CW of the power amplifier MA As aresult windings CW are energized in direction and amount to bias poweramplifier toward cut-01f so that the output voltage at terminals 74, 75of the power amplifier MA is reduced and prevented from materiallyexceeding the selected reference voltage at resistor R.

I am thus enabled to select, for any particular kind or type of grindingjob, a suitable or thereto appropriate voltage to apply across the locusof electric stock removal from the work-piece, a voltage which, forelectrolytic decomposition at the w0rk-face, may be on the order of 10volts or 15 volts, or more, up to about 30 volts; a single manualcontrol, set by the operator, suflices. Voltage may be maintained orregulated for substantial constancy, under certain varying conditions atthe work-wheel interface and, as later described, other controls step inautomatically under other conditions. Effective conduction may bebroken, as by moving the work-piece completely out of relation to theconductive element of the apparatus, as in offhand grinding, orconduction may be interrupted while a work-piece is being removed forreplacement; under such circumstances, the windings RW of the poweramplifier stand substantially de-energized and the voltage across theamplifier output terminal 74, 75, to which the small-load resistance Ris permanently connected, stands at the selected value as determined bythe setting, at resistor R of the energizing current for the biaswindings BW. As described later, I also make provision for guardingagainst current surges or flashes when the work-piece is brought intoconductive relation. Thereafter, so far as voltage constancy isconcerned, certain changes in interface conditions determine thecoaction of the above described parts, such as the energization of poweramplifier win-dings RW to compensate for voltage decline and to maintaingood rate of stock removal so long as the selected interface voltage isnot exceeded and to bring into action the preamplifier windings VW toeffect energization of the power amplifier windings CW to guard againstthe interface calling for and receiving thereacross voltage in excess ofthe selected and appropriate value.

However, and particularly in effecting stock removal by electrolyticdecomposition, it is advantageous to avoid surges and flashes on makingor breaking work-wheel contact and it is desirable to make provisionagainst permitting interface conditions to call for and receivemagnitudes or densities of current as are damaging to the apparatus; forexample, in electrolytic grinding, arc-over, which can be caused in themanner earlier above indicated, can be destructive to the element orelements of the grinding wheel, and such destructive action can beespecially cost-1y where the conductive element is expensive tomanufacture or where it contains costly diamond abrasive grains. Anillustrative and preferred form of controls, coacting with the abovevoltage control, may include the preamplifier MA which I provide withcontrol winding IW, one for each of the reactor units VII, VIII, IX, X,XI, XII, which, as shown in Figure 7, are interconnected, illustrativelyin series, for conjoint or simultaneous energization, their circuitterminating at connecting terminals 121, 122. These I arrange so thatthey will respond to a number of characteristics of interface conditionssuch as those which are conducive to current surges or flashes and suchas call for current increases in excess of a selected safe maxi-- mumcurrent value which can be just below the current value at which harmfulor damaging arcing would occur. For example, makes or breaks at thework-wheel interface under conditions permitting otherwise safe highcurrent values or densities can cause detrimental surges, flashes,arc-overs and the like; also for one type of grinding .job the criticalarcing current value may be 40 amperes, and in such case it may bedesired to limit current rise across the work-wheel interface to a valueof, say, 30 amperes, thus also providing an ample margin of safety.

{\cross the fured or steady unidirectional voltage circurt 86, 87, Ibridge a resistor R' and provide it with a tap as shown so that anyfraction of the voltage drop across the resistance may be selected as astandard against which to measure changes in interface current; bythestructural elements and circuit arrangements above described," includingthe saturable impedance devices 106-CO, the transformer T and therectifier bridge RB current changes across the interface W-CR aretranslated into a substantially proportionately varying unidirectionalvoltage across the circuit 167, 108, and across the latter I bridge aresistor R which I also provide with a tap as shown, so that anyselected fractional part of the voltage drop thereacross may beutilized.

These resistors R R with their respective taps, I arrange in circuitwith the preamplifier windings 1W in such manner that the resistorpotential drops arein opposltion to each other. Coacting and also incircuit with resistors R and R is a resistor R as is later explained, itmodifies the effect which resistor R is to have as against the referencestandard set by resistor R and does so, through means later described,so that when work-wheel interface resistance is low (as because of largecontact area) there can be high current flow across the interface, andvice versa, and so that other advantages are achieved. This circuitextends from preamplifier terminal 121, then by conductor 123, through aprotective resistor R through a unidirectional valve or rectifier UVthrough resistor R through the resistor tap and the selected portion ofthe resistor R conductor 87, conductor 124, selected portion of resistorR and its tap, and then by conductor 125, to the other preamplifierterminal 122.

Disregarding resistor R for the moment, the settings or adjustments, asby setting the tap on resistor R and the tap on resistor R may be-somade that the selected fixed or steady voltage across the selectedportion of resistor R is equal to the voltage across the selectedportion of resistor R when the current across the interface equals theselected safe valuewhich is not to be materir DArsonval torque coil.

ally exceeded, illustratively 30 amperes where the critical ordestructive arcing current is 40 amperes, as assumed in the above givenillustration. Accordingly, so long as the interface current is at orbelow the safe maximum value, the voltage drop at resistor R which isproportional to the interface current, is equal to or less than thereference voltage drop provided by resistor R"; these voltages are inopposite directions in the series circuit of the preamplifier windingsIW, and no current fiows through the latter so long as the referencevoltage at resister R preponderates over the current-responsive voltagedrop at resistor R because the unidirectional valve UV stops or blockscurrent flow in that direction. So long as these conditions exist,varying or changing interface conditions can call upon and effect, bythe arrangements earlier above described, actuation of the poweramplifier windings RW to compensate for declining voltage or to callupon and energize the voltageresponsive windings BW of the preamplifierin turn to energize the control windings CW of the power amplifier tomaintain the work-wheel voltage substantially constant or to preventexcessive rise in that voltage.

Still disregarding resistor R as soon, however, as an interfacecondition arises calling for more than the selected safe maximum currentvalue such as the abovementioned 30 amperes, and sucha condition canillustratively arise as by a substantial increase in interface area orsubstantial and sometimes sudden increase in pressure between the workand wheel, the current-responsive voltage drop across theselectedportion of resistor R exceeds the reference voltage drop at resistor Rand with the former preponderant, current can now flow through thepreamplifier current-responsive windings IW, for the direction of flowis the same as that permitted by the valve or rectifier UV in the abovedescribed series cir cuit, which includes the windings IW. Accordingly,the biasof the'reactor'units of the preamplifier MA is changed to permitor cause current flow at its output terminals 91, 92 to the controlwindings CW of the power amplifier MA in a direction and amount to biasthe power amplifier downwardly toward cut-off and thus hold the currentoutput of the latter and the current across the interface againstmaterially exceeding the selected safe value.

Considering now resistor R in Figure 5, I provide means for making iteffective to supply a unidirectional voltage in a direction subtractivewith respect to the reference voltage drop across resistor R underwork-wheel interface conditions earlier above suggested. In the formshown, I provide two circuits arranged to affect the action of resistorR one of these circuits measures work-wheel resistance and the othermeasures the degree to which detrimental arcing or sparking threatens.

As shown diagrammatically in Figure 5 I provide what is in effect acomputing device to continuously determine the ratio of voltage acrossthe work-wheel interface to the current thereacross, thus always tomeasure interface resistance throughout varying interface conditions; inthe illustrative form shown at 130, this device utilizes anelectrodynamometer multiplying element coacting with a It has a shaft131 suitably pivoted as at 132 and 133 and to which are secured coils134, 135, and 136. Coil 134 operates in or coacts with the magneticfield of a stationary coil 137; coils 135 and 136 operate in orcoactwiththe respective magnetic fields produced by permanent magnets 138 and139. The resultant torque effect upon shaft 131 is translated bysuitable means to control the magnitude of the voltage across resistor Rpreferably by utilizing a light beam and a photocell and amplifierarrangement to respond to changes in the rotary position of shaft 131.Thus, shaft 17 I r 137 carries a mirror 141 which receives light from asuitable source or lamp 142, via a suitable lens or lens systems 143, sothat, according to the rotary shift of shaft 131, as determined by thecoils and their coacting magnetic fields, the beam of light reflected bythe mirror correspondingly affects the conductivity of the photocellsuch as a twin photocell 145 and the resultant current changes amplifiedas by a D. C. amplifier 146 whose D. C. output varies according to therotational shift of shaft 131.

Stationary coil 137 and moving coil 134 together form anelectrodynamometer combination; its moving coil 134 is connected torespond proportionately to the current called for by the work-wheelinterface and for this purpose it is convenient to connect it, byconductors 147 and 148 respectively to the tap and to one end of aresistor R bridged across the circuit 107-108 which is energized asearlier described, by unidirectional potential that is alwayssubstantially proportional to interface current. Moving coil 135 of theDArsonval'combination 135138 is connected to respond proportionately tothe voltage across the work-wheel interface, as by connecting it acrossthe latter by conductors 151, 152. The stationary coil 137 of theelectrodynamometer combination 134-137 is energized by the output of theD. C. amplifier 146, and has the resistor R in series with it, thecircuit being as follows:

:From one output terminal of amplifier 146, conductor 153, stationarycoil 137, conductor 154, resistor R and by conductor 155 back to theother output terminal of the amplifier.

The electrodynamometer 134-137 produces a torque proportional to theproduct of the photocell-amplifier output current and the interfacecurrent across the wheel CR and work W and the DArsonval combination135-138 produces a torque proportional to the voltage across theinterface CR W; the circuit connections are such, in relation to thepolarities involved, that these two torques, in their effects upon theshaft 131 and mirror 141, are opposed, and accordingly the shaft andmirror respond to any difierence between the two, in either direction,and thereby cause corresponding increase or decrease in thephotocell-amplifier output to restore equality and thus maintainbalancing of the opposing torques. The resulted change in unidirectionalcurrent flow in the above-described amplifier circuit effectscorresponding change in the potential drop across the resistor R withresults and actions later described. The twin-photocell and D. C.amplifier arrangement 145146 may be of any suitable or known form orembodiment so that, for whatever position the mirror 141 is given uponbalancing the two opposed coil torques, the D. C. amplifier outputstands at a corresponding value as does also the potential drop acrossresistor R preferably the amplification factor therefor is chosen ormade sufficiently high so that slight or small net coil (and mirror)movements are reflected in substantial amplified output current changes,resulting in rapid responses to changes in the above electricalquantities that affect the torques exerted by the moving coils.

If I is the photocell amplifier output current, then the equation oftorque balance takes the form KE =l I where:

=work-wheel voltage,

l =work-wheel interface current, and K=a proportionality constant.

output current, as above described, is fed through the resistor R insuch direction that the potential drop terface current may increase.

thereacross is in a direction opposite to that across the selectedportion (selected reference voltage value) of resistor R in the circuitcf current-responsive control windings 1W of the current-supply system,being, in the illustrative embodiment here shown, the control windings1W of the pro-amplifier MA whose action was above briefly describedwithout reference to resistor R For clarity, that circuit of resistors Rand R is as follows, bearing in mind that control windings 1W areconnected across pie-amplifier terminals 121122: from erminal 121,conductor 123, protective resistor R unidirectional valve UV resistor Rresistor tap and selected portion of resistor R", conductor 37,conductor 124, selected portion of resistor R and its tap, and byconductor 125 to the other terminal 122. In this series circuit, thereference voltage drop at resistor R is in one direction; it fixes thestandard or value of work-Wheel interface current level beyond whichcontrol windings 1W are to act to prevent material increase. In thatsame series circuit, the voltage drop across resistor R operates in adirection opposite to the voltage drop across resistor R" so as tosubtract from the latter and thereby change or vary the just-mentionedstandard or value of workwheel interface current level against which theworkwheel current responsive voltage drop across selected portion ofresistor R is to act.

When the work-wheel interface resistance is low, as when there is largearea of work-wheel juxtaposition or even smaller such area plussubstantial pressure of contact, it is desirable to maintain highcurrent flow and density at the work-wheel interface for efiecting highrate of stock removal from the work W; with low interface resistance,the photocell-amplifier output current is low as is also the voltagedrop across resistor R and the latter has low subtractive effect uponthe drop across resistor R The net effect of these two resistor drops istherefore to maintain high the standard or limiting value up to whichthe interface current may thus increase or continue at a high level forhigh rate of stock removal. Should interface current commence toincrease above this standard, the current-responsive voltage drop acrossthe selected part of resistor R exceeds the reference voltage which isthe voltage drop at resistor R minus the low or minimum drop acrossresistor R and with drop at resistor R now preponderant, current canflow through control windings IW in the direction permitted by the valveUV in the above circuit, so that the output of preamplifier MA biasesthe power amplifier MA downwardly and thus hold the output of the latterand the interface current from materially exceeding the safe selectedvalueas modified by the resistance across the interface, a resistancewhich, in the above is illustratively low, or at a minimum for a giventype of grinding job. Thus a safe current limit, illustratively of 30amperes may be imposed and automatically maintained.

Now, as conditions at the interface change, as by lessening the area ofcontact or of juxtaposition between work W and wheel CR as when the workis traversed to diminish overlap, thus increasing the interfaceresistance, the electrodynamometer-DArsonval combination faithfullyfollows the resistance change With prompt re sponse to its increments ofchange and causes correspond ing increase in the voltage drop acrossresistor R thus increasing the magnitude of the subtractive voltagefactor in relation to the fixed reference voltage drop across resistor Rand correspondingly shifting in downward direction the standard orlimiting value up to which in- That means that as inter face resistanceincreases as a result of changing interface conditions in a direction toincrease risk were a high level of current value or density to bemaintained, the level at which current is limited is also diminished.Ac-

cordingly, the voltage drop at resistor R becomes constandard in thatthe drop across resistor R is at a higher value (the interfaceresistance being higher) and the difference between the fixed referencevoltage drop across resistor R and the now greater voltage drop acrossresistor R is lower. As a result current can flow through the controlwindings IW in the direction permitted by the valve UV so that theoutput of pro-amplifier MA biases the power amplifier MA furtherdownwardly and hold its output and the interface current from exceedingthe now lower selected value as affected by the increased or higherinterface resistance. In this manner, the current limit level may beautomatically lowered, from the above illustrative ampere level, asinterface resistance increases, down to zero value for open-circuitcondition at the interface, and, of course, reverse operation takesplace to raise the standard at which interface is limited as interfaceresistance decreases, up to the selected maximum level of, say, theabove illustrative 3D ampcres.

These actions are of value and advantage and meet many varyingconditions of practice. For example, there may be relative traversebetween grinding wheel and work-carrying table 24 (Figures 1, 2 and 3),as by longi 'tudinal movement or reciprocation of the table, and in thecourse thereof apparent or actual area of contact between work W andconductive element CR (as well as pressure of contact) may vary; alsothe work W may be run off or run onto the face of ring CR and thesefactors respectively decreased and increased. There may be relativeinfeed movement, as by inward movement or feed of the cross slide 25,and in that manner also variables introduced. Or, where the work W ismanually manipulated, as in offhand grinding or as in the abovementionedPatent 2,381,034, such variables are also introduced; in these cases, aswhen grinding the nose of a tool, work-wheel interface is small andresistance high and frequent makes and breaks, electrically speaking,can take place between work-piece and conductive element. Theelectro-dynamometcr DArsonval elements effect rapid response to thevariables that can come into being under such widely varying conditionsof practical use and with corresponding faithfulness and rapidity set orvary the effective reference voltage (the difference between fixedreference voltage drop at resistor R and the variable voltage drop atresistor R so that a safe current-limit level for whatever conditionarises is automatically set throughout and for the many changes ininterface conditions that can occur while maintaining high rate of stockremoval for that particular condition. On Open circuit, the lowest valueor standard of currentlimit level is set, for with the work out ofeffective conductive relation to the wheel, the resistance is highestand the voltage drop at resistor R is the highest; relative parts andtheir constants may be selected or adjusted so that any desired minimumvalue of currentlimit level may hethus achieved. Here a practicaladvantage is that when Work and wheel are brought into or out ofconductive relation, the current-supply system is automatically at orpromptly brought to its lowest current-limit value and contact may beeffected or interrupted without detrimental reactions such as currentsurges, flashes, or the like; this is particularly advantageous wherethe work-piece is manually manipulated as in off-hand grinding in thecourse of which many makes and breaks may occur.

According to other features of my invention, I am enabled also tomaintain highest or maximum rate of stock removal for or at any of thevarious different work-wheel interface conditions. I noted above, as anillustration, how certain of the controls may be set and operated byproviding a margin of safety, as it were, between the critical arc-overcurrent value at higher levels of operation; say 40 amperes, and aselected safe maximum current value for that level, say 30 amperes,beyond which material current increases are not to take place;.it willbe appreciated that the larger this margin, the less eflicient is thestock removal operation. By arrangements of parts and coactions about tobe described, this margin may be greatly reduced and highest efficiencywith maximum safe current density achieved for whatever interfacecondition exists, with dependable protection against arcing and likedetrimental effects. As above described, the dynamometcr-DArsonvalapparatus is provided also with a torque producing coil i36 operating inthe magnetic field of the permanent magnet 139, as a convenient orsuitable way to modify the torque balancing action above described withrespect to the torque coilsand 134, thus to affect the shift of themirror and the output of the amplifier 146 that energizes the resistor RCoil 136 I arrange to be energized in response to detection of anywork-wheel interface condition that is on the verge of effecting arcingor sparking; threatened or incipient arcing or sparking is made at onceto affect the power supply controls so the detrimental arcing orsparking cannot occur and it does so while maintaining highest currentflow across the interface consistent with no detrimental arcing orsparking, thus establishing, for whatever condition, the narrowestpossible margin between whatever is the critical arcing current for thatcondition and the actual safe current flow. Wide margins on the order ofthe abovementioned illustrative difference between 40 amperes and 30amperes need not be resorted to; instead, for a 40 ampere criticalarcing current which is to be avoided, the apparatus can maintain acurrent flow and thus also higher current density at values closelyapproximating and just short of the critical value and just short ofactual arc'over. Arcing or sparking is accompanied by large increase influctuation of both interface current and interface voltage. Duringnormal or not: arcing and non-sparking stock-removal operation, eventhough interface voltage and current stand or are at substantiallyconstant effective values for any given inter face condition, theelectrical action in stock removal is reflected in fluctuations ininstantaneous values of vol tagc and current and these occur atrelatively low frequencies. but when arcing or sparking occurs, thesefluctuations in instantaneous values take place at much highcfrequencies, frequencies on the order of several hundred er second andhigher, and the transition from non-arcing or sparking is accompanied byintermediate rise or increase in frequency of these fluctuations. Acondition of threatened or incipient arcing or sparking may thus bedetected by frequencies within the transition range of change offrequency. Tell-talc frequency, corresponding to threatened or incipientarcing or sparking, is within the range of about 350 to 500 cycles.

Accordingly, I provide a high-pass filter 161' and connect it across thework-wheel interface by conductors 161, 162, with a series capacitor 163in the connecting circuit to block flow of unidirectional current fromthe D. C. interface circuit while permitting the filter 169 to respondto the components of the interface electrical fluctuations. This filtercan have a cut-off or blocking action to all frequencies belowfrequencies of from about 350 cycles per second to about 500 cycles sothat it passes on to an A. C. amplifier 164 which may be of any suitableor known form and need not be shown or described in detail, all higherfrequencies. its transition or cutoff characteristic may be relativelysteep for a selected frequency in the above range or for a selectednarrow band of frequencies within that range or it may have substantialslope, covering a substantial spread or band of frequencies in thatrange, preferably the former in order to give, at its output and at theoutput of the amplifier 164, a rapid and relatively powerful response tofrequency increase corresponding to incipient arcing or sparking.Suitable plate and other voltages for the internal circuit of amplifier164 may be derived from the steady voltage circuit 8485 and the same istrue as to the D. C. amplifier 146 and its photocell circuit; bothamplifiers are shown as, connected to steady voltage circuit 8485 forthese purposes.

The amplified output of amplifier 164 is passed to the input of afull-wave rectifier RB whose rectified output is connected by conductors166, 167 to the DArsonval torque coil 136 on the torque-balancingmetering unit 130 above described, with such regard for polarities thatthe torque effect produced by coil 136, in response as above describedto interface conditions threatening or about to invite detrimentalarcing or. sparking, is in a direction the same as that of interfacevoltage torque coil 135' and opposite to that of coil 134 of theelectrodynamometer 134137. Torque coil 136, when so energized, causespivotal shift of the shaft 131 and mirror 141 of the position at whichtorque-balance has to occur by increased output, initiated by thechanged light effect of mirror 141 on the twin photocell 145, of thephotocell-amplifier 145-446 to the dynamometer movable coil 134, thuscausing increased current flow to the resistor R and increase in thevoltage drop thereacross. That, as will now be clear, decreases thedifference between the selected fixed reference voltage drop at resistorR' and the just mentioned increased voltage drop across resistor Rimmediately preventing rise of and slightly lowering the current-limitlevel of the power supply to the work-wheel interface, as by the actionof current-control windings 1W upon the pre-amplifier AM and resultantcontrol of the current output of the power amplifier AM It will be notedthat by the resultant action and effect, a lowering of the current-limitlevel down to some arbitrary or selected level need not be had toprovide a wide margin of safety between critical arcing current andactual interface current; instead the action and result can be tomaintain the highest interface current just bordering on incipienceof.detrimental arcing or sparking even as incipient conditions vary orchange from moment to moment, and thus maximum efficiency and capacityof stockremoval may be maintained with dependable protection againstdamaging arcing or sparking. For example, as the work-piece, in itstraverse, is gradually run off of the conductive wheel element CR thusprogressively diminishing overlap or area of contact between the twountil there is complete interruption of conduction therebetween, eachincrement j of such relative movement betweenwork and wheel, whileachieving progressive lowering of the current-limit level by thecoactions of the balancing torque'coils 135 and 134 asearlier abovedescribed in response to changes in interface resistance, tends toencourage possibility of arcing or sparking inasmuch as, withdiminishing juxtaposed areas of apparent or real contact, currentdensities tend to increase and that is conducive to localized currentconcentrations in turn conducive to arcing or sparking; nevertheless, bythe action of torque coil 136 and its response to interface frequenciesof incipient arcing, arc-over is prevented while maintaining alwayshighest possible current flow and density for any momentary interfacecondition as traverse continues, and this proceeds throughout the widerange of change in interface conditions as traverse continues, alwaysadjusting current-limit level to the changes. Con verse actions andcontrols for safety and for maximum efficiency take place on reversestroke of the workpiece, as when it is first brought at one end intocontact with the conductive wheel element and their overlapprogressively increased; here initial conduction takes place safely atlowest current-limit level as above earlier described, and that level isprogressively raised with increase in overlap as dictated by changes atthe interface and may be held at just below arcing or sparkingincipience according to whatever is the changing or instantaneouscondition at the work-wheel interface. Thus it is possible to maintainthe current limit level at a point or value where threatened orincipient arcing a y 22 or sparking cannot reach a magnitude damaging orde-' structive of apparatus, and thus efliciency and capacity of stockremoval materially enhanced. I

The system and apparatus provided in this invention will thus be seen toachieve the various objects above noted or indicated, together with manythoroughly practical advantages. The widely varying work-Wheel interfaceconditions eifect dependable control of the electrical energy suppliedthereto and thus the apparatus and system can readily meet the many andvaried requirements met with in many and various types of grindingoperatious; this is furthermore achieved in a manner not only to providedependable protective action but also to effect and maintain highefliciency of action. Moreover, where the plant or factory is alreadyequipped withalternating current energy supply, these and many otheradvantages are attained bydependable and flexible controls by theinterface conditions of the conversion of the alternating current energyto direct current energy.

Current and voltage values at the work-wheel interface or interface setout above will be understood to be illustrative, for by the variouscircuit arrangements and adjusting devices, such as adjustable taps onresistors and transformer windings, a wide range of standards ofoperation at other current or voltage values is achievable according tothe particular grinding operation or requirements to be met. However,the apparatus and system, when once adjusted or set, functionsautomatically and in a self-accommodating manner, so far as theoperation is concerned, in shifting the system and apparatus to meet therequirements, for example, another type of grinding job, for all theoperator need do in such a case is to set the voltage-standard resistorR at its tap, and he need not make any other readjustments.

Also, in other respects the system and apparatus pro- Vides flexibility;for example, the above-described setting of resistor R may be made sothat the bias windings BW bias the power amplifier PW forfull-conduction rather than to provide, as in the above illustration,the selected voltage, at its output terminals 74, 75, whereuponregulation of the output voltage proceeds under the action and controlof the voltage-compensating control windings RW and of the controlwindings CW as the latter are in turn controlled by thevoltage-responsive windings VW of the pre-amplifier MA Such setting ispreferred where the voltage-compensating windings RW are, as is usuallythe case, relatively not too powerful, acting principally to add only arelatively small positive bias in order appropriately to compensate forvoltage drop in response to current increase, and vice versa, and wherethe voltagecontrolled response of the windings CW do not contributepositivebias because of the blocking action of the rectifier UV. i

In any case, so far as the operator is concerned, the apparatus may beby him operated and controlled with few and simple panel controls which,in view of all of the foregoing, will be seen to be the single tapcontrol for resistor R with, of course, a main on-olf switch.

The system and apparatus will thus be seen to be thoroughly practical,dependable and well adapted to achieve dependable self-protection andsafety of use or operation throughout widely varying conditions met within practice.

As many possible embodiments may be made of the mechanical features ofthe aboveinvention, and as the art herein described might be varied invarious parts, all without departing from the scope of the invention, itis to be understood that all matter hereinabove set forth, or shown inthe accompanying drawings, is to be interpreted as illustrative and notin a limiting sense.

- I claim:

1. In electrolytic grinding apparatus, in combination a work-support androtatable .wheel means having a conductive part whereby a conductivework-piece and the face of the wheel conductive part are interrelatedfor agen as relative movement therebetween, with means for supplyingliquid electrolyte to the interface between the workpiece and saidconductive part for electrolytic decomposition at the work-piece face, asaturable-core magnetic amplifier having power Winding means energizedby alternating current and having rectifier means in circuit therewithto provide unidirectional current at its output terminals and havingcontrol winding means for affecting the core saturation thereof, asatnrable-core control magnetic amplifier having power winding meansenergized by alternating current and having rectifier means in circuittherewith for energizing said control winding means of said firstmagnetic amplifier and having control winding means for affecting itsown core saturation, means connecting the positive side of said outputterminals to the work-piece and the negative side thereof to said wheelconductive part for effecting electrolytic decomposition at thework-piece face, means responsive to interface current, means responsiveto the potential across said interface, means correlating said twolast-mentioned means to convert their respective responses into ameasore of interface resistance, means for energizing said secondcontrol winding means in accordance substantially with changes in saidmeasure of interface resistance to effect responsive amplification bysaid control amplifier of the energy the latter supplies to said firstcontrol winding means and thereby to vary the current at said outputterminals of said first amplifier substantially inversely to interfaceresistance changes, frequency-responsive means electro-responsivelyinter-related with said interface and responsive to electricalfluctuations at the interface of frequency values caused by incipienceof arcing or sparking across the interface, and means controlled by saidfrequency responsive means for limiting current output at said terminalsto a value just short of arc-over or sparking at said interface.

2. In apparatus as claimed in claim 1 in which said last-mentioned meanscomprises means operating upon said correlating means to raise itsstandard of conversion into resistance measurement.

3. In electrolytic grinding apparatus, in combination, a work supportand a conductive rotatable member whereby a conductive work-piece andsaid member are interrelated for relative movement therebetween, withmeans for supplying electrolyte to the, interface between the workpieceand said member for electrolytic decomposition at the work-piece face, asaturable-core magnetic amplifier having power winding means energizedby alternating current and having rectifier means in circuit therewithto provide unidirectional current at its output terminals and havingcontrol winding means for affecting the core saturation thereof, asaturable-core control magnetic amplifier having power winding meansenergized by alternating current and having rectifier means in circuittherewith for energizing said control winding means of said firstmagnetic amplifier and having control winding means for affecting itsown core saturation, means connecting the positive side of said outputterminals to the work-piece and the negative side to said conductivemember to provide for electrolytic decomposition at the work-piece face,means responsive to interface current changes for affecting said firstcontrol winding means in a direction to substantially maintain thevoltage across said interface against changes caused by changes incurrent demanded thereby, means respon sive to changes in voltage acrossthe interface above a selected value for energizing said control windingmeans of said control amplifier to affect its energy supply to saidpower amplifier control winding means and thereby prevent substantialupward departures in voltage across said interface whereby currentdemanded thereby may vary with interface conditions, interfacecurrent-responsive means and means responsive to the potential acrossthe interface with means integrating their respective responses intosubstantially a measure of interface re- 24 sistance throughout changesin interface conditions, means for energizing said control winding meansof said control amplifier in response to interface currents above aselected value to effect current-limiting at said output terminals, andmeans for modifying the action of said last-mentioned means to shift thelevel of current-limiting in response to said measure of interfaceresistance.

4. An apparatus as claimed in claim 3 in which said last-mentioned meansfor energizing said control winding means comprises a circuit providinga reference voltage in series with a unidirectional valve and a resistorproviding a voltage drop substantially proportional to interface currentand in which said modifying means comprises means responsive to changesin said measure of interface resistance for affecting the coactionbetween said reference voltage and said resistor in said last mentionedcircuit.

5. An apparatus as claimed in claim 4 in which said last-mentioned meanscomprises a resistor energized in inverse response to changes in saidmeasure of interface resistance and thereby providing a voltage dropvarying inversely as said interface resistance, said last-mentionedresistor being connected in the circuit of said reference voltage andsaid resistor with its voltage drop acting in a direction opposite tothat of said reference voltage.

6. In apparatus for electrical stock removal from a conductivework-piece, in combination, means for effect ing stock removal from aconductive work-piece by electric current flow from the work-piece facecomprising conductive means and means including a work support forinterrelating the conductive means and the workpiece for relativemovement therebetween during stock removal and thereby providing aninterface between the work-piece and said conductive means of variableelectrical resistance as interface conditions change during stockremoval, means for supplying electrical energy to the interface betweenthe work-piece and said conductive means comprising electromagneticpower Winding means energized by alternating current and having itsoutput connected by conductors to said work-piece and said conductivemeans with means for varying the output energy comprising saturable coremeans having control winding means adapted upon change in energizationto change the magnetic saturation of said core means and therebyincrease or decrease the current of said output energy according to thedirection of change of energization of said control winding means, andmeans for varying the output current of said energy-supplying meanssubstantially inversely to said interface resistance variationcomprising a metering device for measuring interface resistance andhaving means connected to respond to changes in interface current andmeans connected to respond to changes in interface voltage with meansintegrating the two to evaluate resistance, means for energizing saidcontrol winding means with means responsive to changes in said evaluatedresistance to vary the energization of said control winding means indirection to decrease said current output upon increase in saidresistance and to increase said current output upon decrease of saidresistance.

7. In an apparatus for electrical stock removal from a conductivework-piece, in combination, a work-support for the work-piece, aconductive part for coaction in electric stock removal from theworkpiece face and providing with the latter an interface at whichconditions are variable as relative movement takes place between theworkpiece and said conductive part, means for supplying electricalenergy having its output connected to said conductive part and to thework-piece and having control means adapted to affect the voltage andcurrent of the energy delivered to said interface, means adapted toaffect said control means in directions to maintain substantiallyconstant the voltage across said interface whereby interface current mayvary as interface conditions change, means responsive to changes ininterface current above a selected 25 I value for affecting said controlmeans in direction to effect current-limiting action upon said sourceand thereby limit interface current, said last-mentioned meanscomprising means providing a selectable reference potential forselecting the value at which interface current is limited as a maximum,interface current-responsive means and means responsiveto the potentialacross the interface with means integrating their respective responsesinto substantially a measure of interface resistance throughout changesin interface conditions, and means for modifying the action of saidreference-voltage means to shift the level of current-limiting inresponse to said measure of interface resistance.

8. In an apparatus for electrical stock removal from a conductiveWork-piece, in combination, a work-support for the work-piece, aconductive part for coaction in electric stock removal from theworkpiece face and providing with the latter an interface at whichconditions are variable as relative movement takes place between theworkpiece and said conductive part, means for supplying electricalenergy having its output connected to said conductive part and to thework-piece and having control means adapted to affect the voltage andcurrent of the energy delivered to said interface, means adapted toaffect said control means in direction to maintain substantiallyconstant the voltage across said interface whereby interface current mayvary as interface conditions change, means responsive to changes ininterface current above a selected value for affecting said controlmeans in direction to effect current-limiting action upon said sourceand thereby limit interface current, and means responsive to changes ininterface resistance for affecting said control means in direction todepress the level of said current-limiting action as interfaceresistance increases and operating reversely upon subsequent decreasesin interface resistance, said interface-resistance-responsive meanscomprising opposing torque coils with means for energizing one of themproportionately to interface current and with means for energizing theother proportionately to interface voltage and means providing saidtorque coils with respective magnetic fields of which one comprises anelectromagnetic winding adapted to be variably energized to achievebalance, means variable according to and responsive to the conjointeffects of said opposing torque coils to achieve balance of torque forenergizing said winding, said means for affecting said control meanscomprising means responsive substantially. proportionately to thevariable energization of said windmg.

9. In apparatus for electrical stock removal from a conductivework-piece, in combination, means for effecting stock removal from aconductive work-piece by electric current flow from the work-piece facecomprising conductive means and means including a work-support forinterrelating the conductive means and the workpiece for relativemovement therebetween during stock removal, and means for supplyingunidirectional electrical energy to the interface between the work-pieceand said conductive means and having control means for affecting thesupply of electrical energy to said interface, said control meanscomprising opposing torque coils with means for energizing one of themproportionately to interface current and with means for energizing theother proportionately to interface voltage and means providing saidtorque coils with respective magnetic fields of which one comprises anelectro-magnetic winding adapted to be variably energized to achievebalance, means variable according to and responsive to the conjointeffects of said opposing torque coils to achieve balance of torque forenergizing said winding, and means for controlling said control meanscomprising means responsive substantially proportionately to thevariable energization of said winding.

10. An apparatus as claimed in claim 15 in which there is provided athird torque coil with means providing V 26 a it with a magnetic fieldto exert torque in a direction op posite to that exerted by the torquecoil that is energized proportionately to interface current,frequency-responsive means having means relating it to the interface forresponse to changes in frequency, caused by changes in electricalconditions at said interface, of fluctuations in instantaneouselectrical values caused by incipience of arc-over at the interface, andmeans controlled by said frequency-responsive means for energizing saidthird torque coil and thereby changing the standard of coactingoperation of said first-mentioned opposing torque coils.

11. An apparatus as claimed in claim 10 in which saidfrequency-responsive means comprises amplifying means having an outputconnected to control the energization of said third torque coil andhaving an input with means interposed between said interface and saidinput for detecting changes in frequencies caused by fluctuations ininstantaneous electrical values corresponding to incipience ofdetrimental arcing or undesired sparking at said interface.

12. In an apparatus for electrical stock removal from a conductivework-piece, in combination, a work-support for the work-piece, aconductive part for coaction in electric stock removal from thework-piece face and providing with the latter an interface at whichconditions are variable as relative movement takes place between thework-piece and said conductive part, means for supplying electricalenergy having its output connected to said conductive part and to theWork-piece, regulating means operating upon said supply means forcontrolling the value of a function of the electrical energy deliveredat said output and variably dissipated at said interface during saidstock removal and during said relative movement, and means comprising acomputing device having means responsive to changes in potential acrosssaid interface and having means responsive to changes in interfacecurrent and having means integrating the resultant potential and currentchanges substantially into the quotient of interface potential andinterface current, and means responding substantially proportionally tochanges in said quotient for affecting said controlling means and causeit to regulate said function of said electrical energy at a dififerentvalue.

13. In an apparatus for electrical stock removal from a conductivework-piece, in combination, a work-support for the work-piece, aconductive part for coaction in electric stock removal from thework-piece face and providing with the latter an interface at whichconditions are variable as relative movement takes place between thework-piece and said conductive part, means for supplying electricalenergy having its output connected to said conductive part and to thework-piece, control means adapted to affect the value of a function ofthe electrical energy delivered to said interface, said control meanscomprising a circuit providing a reference voltage in series with aunidirectional valve and a resistor, means responsive to changingelectrical conditions at said interface for substantially measuringaccompanying changes in interface resistance, means for supplyingelectrical energy to said resistor to provide an IR drop in said seriescircuit, and means responsive to said resistance-measuring means forsubstantially proportionally changing the energy supplied to saidresistor and thereby affecting the coaction between said referencevoltage and said resistor and said control means to change the currentdelivered to said interface substantially inversely as interfaceresistance changes.

14. In an apparatus for electrical stock removal from a conductivework-piece, in combination, a work-support for the work-piece, aconductive part for coaction in electric stock removal from thework-piece face and providing with the latter an interface at whichconditions are variable as relative movement takes place between thework-piece'and said conductive part, means for supplying electricalenergy having its output connected to said conductive part and to thework-piece, control means adapted to affect the value of a function ofthe electrical energy delivered to said interface, means responsive tochanging electrical conditions at said interface for substantiallymeasuring accompanying changes in interface resistance, and meansresponsive to said resistancemeasuring means and operating upon saidcontrol means to change the current delivered to said interfacesubstantially inversely as interface resistance changes, saidresistance-measuring means comprising opposing torque coils With meansfor energizing one of them proportionately to interface current and withmeans for energizing the other proportionately to interface voltage andmeans providing said torque coils with respective magnetic fields ofwhich one comprises an electromagnetic winding adapted to be variablyenergized to achieve balance, means variable according to and responsiveto the conjoint eifects of said opposing torque coils to achieve balanceof torque for energizing said Winding, said means for effecting saidcontrol means comprising means responsive substantially proportionatelyto the variable energization of said winding.

15. in, an apparatus for electrical stock removal from a conductivework-piece, in combination, a work-support for the work-piece, aconductive part for coaction in electric stock removal from theWork-piece face and providing with the latter an interface at whichconditions are variable as relative movement takes place between theWorkpiece and said conductive part, means for supplying electricalenergy having its output connected to said conductive part and to thework-piece, control means adapted to affect the value of a function ofthe electrical energy delivered to said interface, means responsive tochanging electrical conditions at said interface for substantiallymeasuring accompanying changes in interface resistance, saidlast-mentioned means comprising means responsive to changes in thepotential across said interface and means responsive to changes incurrent flow across said interface with means correlating said twolast-mentioned means to convert their respective responses into ameasure of interface resistance, means responsive to said resistance-Ineasuring means and operating upon said control means to change thecurrent delivered to said interface substantially inversely as interfaceresistance changes, means lectrically associated With said interface andresponsive to frequency changes effected by changes in electricalinterface conditions, and means controlled by said frequency-responsivemeans for affecting said control means in direction to limit currentflow across said interface.

References Cited in the file of this patent UNITED STATES PATENTS2,092,859 Seaverson Sept. 14, i937 2,084,870 Schmidt June 10, 19412,245,192 Gugel June 10, 1941 2,287,755 Barth June 23, 1942 2,488,856Few Nov. 22, 1949 2,545,413 Ferret-Bit Mar. 13, 1951 2,547,615 BedfordApr. 3, 1951 OTHER REFERENCES Keeleric: Steel, Mar. 17, 1952, vol. 130,No. 3, pp. 84 to 86, article entitled Electrolytic Grinding.

New Processes For Machining and Grinding, Report No. MAB-18-M ofNational Research Council, Jan. 18, 1952, appendix VI, pages 1 to 9 andFigs. 1 to 4.

1. IN ELECTROLYTIC GRINDING APPARATUS, IN COMBINATION A WORK-SUPPORT ANDROTATABLE WHEEL MEANS HAVING A CONDUCTIVE PART WHEREBY A CONDUCTIVEWORK-PIECE AND THE FACE OF THE WHEEL CONDUCTIVE PART ARE INTERRELATEDFOR RELATIVE MOVEMENT THEREBETWEEN, WITH MEANS FOR SUPPLYING LIQUIDELECTROLYTE TO THE INTERFACE BETWEEN THE WORKPIECE AND SAID CONDUCTIVEPART FOR ELECTROLYTIC DECOMPOSITION AT THE WORK-PIECE FACE, ASATURABLE-CORE MAGNETIC AMPILIFER HAVING POWER WINDING MEANS ENERGIZEDBY ALTERNATING CURRENT AND HAVING RECTIFER MEANS IN CIRCUIT THEREWITH TOPROVIDE UNIDIRECTIONAL CURRENT AT ITS OUTPUT TERMINALS AND HAVINGCONTROL WINDING MEANS FOR AFFECTING THE CORE SATURATION THEREOF, ASATURABLE-CORE CONTROL MAGNETIC AMPLIFER HAVING POWER WINDING MEANSENERGIZED BY ALTERNATING CURRENT AND HAVING RECTIFER MEANS IN CIRCUITTHEREWITH FOR ENERGIZING SAID CONTROL WINDING MEANS OF SAID FIRSTMAGNETIC AMPLIFER AND HAVING CONTROL WINDING MEANS FOR AFFECTING ITS OWNCORE SATURATION, MEANS CONNECTING THE POSITIVE SIDE OF SAID OUTPUTTERMINALS TO THE WORK-PIECE AND THE NEGATIVE SIDE THEREOF TO SAID WHEELCONDUCTIVE PART FOR EFFECTING ELECTROLYTIC DECOMPOSITION AT THEWORK-PIECE FACE, MEANS RESPONSIVE TO INTERFACE CURRENT, MEANS RESPONSIVETO THE POTENTIAL ACROSS SAID INTERFACE, MEANS CORRELATING SAID TWOLAST-MENTIONED MEANS TO CONVERT THEIR RESPECTIVE RESPONSES INTO AMEASURE OF INTERFACE RESISANT, MEANS FOR ENERGIZING SAID SECOND CONTROLWINDING MEANS IN ACCORDANCE SUBSTANTIALLY WITH CHANGES IN SAID MEASUREOF INTERFACE RESISTANCE TO EFFECT RESPONSIVE AMPLIFICATION BY SAIDCONTROL AMPLIFER OF THE ENERGY THE LATTER SUPPLIES TO SAID FIRST CONTROLWINDING MEANS AND THEREBY TO VARY THE CURRENT AT SAID OUTPUT TERMINALSOF SAID FIRST AMPLIFER SUBSTANTIALLY INVERSELY TO INTERFACE RESISTANCECHANGES, FREQUENCY-RESPONSIVE MEANS ELECTRO-RESPONSIVELY INTER-RELATEDWITH SAID INTERFACE OF RESPONSIVE TO ELECTRICAL FLUCTUATIONS AT THEINTERFACE OF FREQUENCY VALUES CAUSED BY INCIPIENCE OF ARCING OR SPARKINGACROSS THE INTERFACE, AND MEANS CONTROLLED BY SAID FREQUENCY RESPONSIVEMEANS FOR LIMITING CURRENT OUTPUT AT SAID TERMINALS TO A VALUE JUSTSHORT OF ARC-OVER OR SPARKING AT SAID INTERFACE.